A and $B$ are two identical balls attached to strings as shown. A is released from position OA. A collides with B elastically. Then,
(a) $\mathrm{A}$ and $\mathrm{B}$ move with different non-zero velocities
(b) $\mathrm{B}$ moves forward and $\mathrm{A}$ rebounds with the same velocity
(c) A and B stick together and move with same velocity
(d) A comes to rest and $B$ moves with the velocity of $A$